The present invention relates generally to compact optical systems and, more particularly, to compact optical systems for use in display devices, for example, personal devices such as wearable personal computer systems, head mounted displays, portable telephones and the like.
Virtual image displays combine magnifying optics with a small image panel to provide the viewer with a virtual image capable of displaying large amounts of information. Such displays have found application in so called head mounted displays and are used in conjunction with a computer-based device for a variety of applications. As is known, the computer-based device includes processing and display driver circuitry for generating the image signal to be displayed via the optics and image panel.
However, such conventional virtual image displays are known to have many shortcomings. For example, such displays have suffered from being too heavy for comfortable use, as well as too large so as to be obtrusive, distracting, and even disorienting. These defects stem from, among other things, the incorporation of relatively large optics systems within the mounting structures, as well as physical designs which fail to adequately take into account such important human factors as size, shape, weight, etc.
Examples of some conventional head mounted virtual displays are shown in FIGS. 1 and 2. FIG. 1 illustrates a head mounted virtual display unit 10 which rests on the users head and face in a manner similar to that of a pair of eye glasses. The user views virtual images through the display portion 12. Nose bridge 14 and side supports 16 serve to provide support for the display while on the users head and face. The unit 10 may be connected to a computer via connector 18. It is known that such a unit is cumbersome and permits the wearer to see substantially nothing other than the display screen. That is, the user is unable to view his immediate environment. Such a head mounted virtual display is disclosed in an international patent application identified as WO 95/11473, the disclosure of which is incorporated herein by reference.
FIG. 2 illustrates a head mounted monocular virtual display unit 20. The support structure 12 is positioned on a users head and the display portion 14 comes down in the users field of vision. This design is also known to be cumbersome and likely to obstruct the users surrounding view. Such a head mounted monocular virtual display is also disclosed in a the international patent application identified as WO 95/11473.
Other examples of conventional compact display systems and head mounted displays are disclosed in U.S. Pat. No. 5,771,124 to Kintz et al., U.S. Pat. No. 5,757,339 to Williams et al., and U.S. Pat. No. 5,844,656 to Ronzani et al., the disclosures of which are incorporated herein by reference. Still further, it is known that Sony Corporation makes a head mounted virtual display known as the xe2x80x9cGlasstron.xe2x80x9d
However, all of the examples given suffer from one or more of the above-mentioned design deficiencies. As a result, such deficiencies have seriously hindered the general acceptance of such devices.
Compact optical systems for use in virtual display applications which improve upon the previously existing art are described in two U.S. patent applications assigned to the present assignee and identified as U.S. Ser. Nos. 09/437,972 and 09/437,793, both filed on Nov. 10, 1999, the disclosures of which are incorporated herein by reference.
Nonetheless, there is a need for a compact optical system for use in display devices, for example, personal devices such as wearable personal computers, head mounted displays, portable telephones and the like, which substantially reduces or eliminates the above-mentioned deficiencies as well as others not specifically mentioned associated with the existing art, and/or which improves upon the compact optical system designs described in the above-referenced U.S. patent applications identified as U.S. Ser. Nos. 09/437,972 and 09/437,793.
The present invention provides an optical system design for use in display devices such as, for example, a head mounted virtual image display, that remedies defects exhibited by conventional designs, e.g., prohibitive size and weight, obstructed view, etc. Such a novel design, for example, makes possible wearable computer systems of greater convenience and acceptability to a wide range of users.
In accordance with one embodiment of a compact optical system of the invention for directing an image signal for viewing by a user, wherein the image signal is generated in accordance with a microdispay, the optical system comprises: a beam splitting prism positioned proximate to the microdisplay; a field lens positioned between the beam splitting prism and the microdisplay; a negative lens positioned between the field lens and the beam splitting prism; a reflective lens positioned proximate to the beam splitting prism, on a side of the beam splitting prism opposite the microdisplay; and a quarter wave plate positioned between the reflective lens and the beam splitting prism; wherein the beam splitting prism, the field lens, the negative lens, the reflective lens and the quarter wave plate are arranged such that the image signal, linearly polarized in accordance with the microdisplay: (a) passes through the field lens and the negative lens; (b) enters the beam splitting prism substantially passing through a polarizing surface of the beam splitting prism; (c) passes through the quarter wave plate becoming circularly polarized; (d) reflects at a surface of the reflective lens back toward the quarter wave plate passing through the quarter wave plate a second time becoming linearly polarized with a polarization direction rotated by 90 degrees with respect to an original linear polarization direction associated with the image signal; and (e) reenters the beam splitting prism substantially reflecting at the polarizing surface of the beam splitting prism and exits the beam splitting prism for viewing by the user.
In accordance with one embodiment of a head mounted virtual image display unit according to the invention, the display unit is compact in size and weight, and incorporates a high performance optical system, such as the optical system described above, offering a clear see-through capability. A sliding light shield may be incorporated for those instances when see-through capability is not desired. A focus adjustment may be incorporated to permit the focusing of the image, for example, at a distance of approximately 18 inches to infinity. An adjustable headband may be incorporated that adapts to fit the users head. A flexible boom structure may be incorporated to facilitate fine positional adjustment of the optical assembly. A slider and ball joint mechanism may also be incorporated to facilitate positional adjustment of the optical assembly. A built-in microphone may be incorporated to enable speech input by the user.
It is to be appreciated that the head mounted virtual image display unit may be used comfortably in conjunction with eye or safety glasses, and provides a useful image to the user without blocking his view of the surrounding environment. The unit is designed to have a pleasing appearance so as to greatly enhance user acceptability.
It is to be further appreciated that a head mounted virtual image display unit may be combined with a computer-based device. The computer-based device may generate and provide an electrical signal to a microdisplay associated with the display unit for use in generating the image signal to be viewed by the user. The combination advantageously forms a portable computer system.